Conventionally, a time deviation is caused with the lapse of time in a clock that contains an oscillator such as a quartz resonator, unless correction of some kind is applied thereto (refer to Japanese Unexamined Patent Application Publication No. 2009-180511, for example). When it is necessary to perform measurement or the like at the correct time in a more precise manner, the measurement or the like is performed while receiving highly accurate time information by GPS radio waves. Further, when it is necessary to perform the measurement simultaneously at a plurality of measurement points, securing simultaneity in the measurement becomes important (refer to Japanese Patent No. 2553689, Japanese Examined Patent Application Publication No. H07-120973, and Japanese Unexamined Patent Application Publication No. 2007-206848, for example), and the simultaneity is secured by connecting a plurality of measuring devices via a cable and the like.
When a switchboard is repaired or remodeled in a power station and a substation, for example, a voltage current transformer (VCT) is used to perform a VCT combination test and a voltage matching test (refer to Japanese Unexamined Patent Application Publication No. 2000-78711, for example). As it is necessary for these tests to obtain a phase difference in voltage and current between the measurement point on a reference side and the measurement point on a comparison side, the voltage and the current are measured at the measurement point on the reference side and the measurement point on the comparison side simultaneously. At this time, the simultaneity in the measurement is secured by connecting the measuring device on the reference side and the measuring device on the comparison side via the cable and the like. Although it is possible to allow the plurality of measuring devices to communicate with each other wirelessly via an FM communication system, it is difficult to secure the simultaneity as a time lag is caused at the time of modulating/demodulating radio signals.